Magnetic field sensors are widely used in incremental speed and position measurement. They detect changes in a magnetic field that is caused by a moving or rotating magnetic encoder.
For example, to measure a wheel speed (e.g., in an automotive application) typically an encoder wheel is used in combination with a magnetic sensitive sensor. The sensor generates an output signal based on a sensed magnetic field that oscillates between two extrema (e.g., a minimum and maximum) in accordance with the rotation of the encoder wheel. A control unit is able to calculate a wheel-speed and an actual angle of the rotating encoder wheel based on the output signals generated by the sensor.
The measurement of the sensed magnetic field may be done differentially between two magnetic field sensor elements of the sensor. The sensor switches between a high and a low state of its output when a threshold crossing in the sensed magnetic field is detected. However, invalid switching events may occur from false crossings due to, for example, signal distortion or reduced amplitudes of single encoder marks. Furthermore, there is no failure fallback scheme is provided with respect to faults of the magnetic sensor elements (e.g., should one of the magnet sensor elements fail).
Therefore, an improved device that is capable of avoiding invalid switching events and that implements a failure fallback scheme may be desirable.